The present invention relates generally to processing of communications signals and, more particularly, to a system and method to perform decimated noise estimation and/or beamforming for use in a communications system.
Various techniques have been developed to facilitate communication of data signals over an associated communications path. The particular communications protocol employed generally depends on the transmission medium, the available bandwidth resources, and other design considerations. Regardless of the type of communications system being employed, noise and distortion often are introduced into data signals transmitted over an associated communications path, including both wired and wireless systems.
Wireless communications systems, such as cellular and personal communications systems, operate over limited spectral bandwidths. Accordingly, multiple access protocols have been developed and used in wireless communications systems to increase bandwidth efficiency. Examples of multiple carrier protocols include Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), and Space Division Multiple Access (SDMA). A particular type of FDMA protocol is Orthogonal Frequency Division Multiplexing (OFDM). Features from these and other multiple-access techniques also have been combined in an effort to make highly efficient use of the scarce bandwidth resource to increase the quality of service.
In a wireless system, in which data signals are transmitted through space as modulated electromagnetic waves, distortion and noise can result from interference with other signals within the same frequency range and path as well as multipath dispersions. Multipath dispersions occur when signals propagate along different or reflected paths through a transmission medium to a receiving destination. For example, radio transmissions or data signals that travel through the space can be reflected off trees, vehicles, houses, larger buildings, and terrain features such as mountains and hills. The radio transmissions further are subjected to fading and interference. Fading involves fluctuations in amplitude of a signal, while interference involves unwanted frequencies in the same frequency band.
Multipath scattering effects alter or distort the signal spectrum when compared to the spectrum as transmitted. The effects are different at different frequencies across the signaling band. At some frequencies, the multipath signals add constructively to result in an increased signal amplitude, while at other frequencies the multipath signals add destructively (out of phase) to cancel or partially cancel the signal, resulting in reduced signal amplitude.
A wireless communication system is designed to compensate for interference due to noise and the deleterious effects of multipath dispersion. However, in order to compensate for the noise, an indication of the noise in the signal must first be determined. Thus, it is desirable to know how much noise and/or interference is present in the system. Generally, noise can be measured relative to the signal as a ratio, such as a signal-to-noise ratio (SNR) and a signal-to-interference-to-noise ratio (SINR). The noise/interference levels are monitored and used to facilitate demodulation of the incoming signal, such as by assigning a confidence level to the data tones of the received signal. Accordingly, it is desirable to efficiently and accurately estimate the noise/interference in a received signal.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
One aspect of the present invention provides a noise estimation system for a communications system capable of improving system performance. The noise estimation system includes a selector that selects a subset of data tones (or carrier tone frequencies) from a given data burst. Noise estimates are computed for the data tones in the selected subset. The noise estimates can be used to update previously computed noise estimates. By controlling how the data tones in each subset are selected, such as based on a burst counter that monitors the received data bursts or other criteria, one can reduce the number of calculations required for each data burst.
For example, the noise estimates can be performed at every other, every fourth, or every nth data tone, where n is a natural number (e.g., an integer greater than 0). Alternatively, data tones can be organized into consecutive subsets of data tones. After the noise estimates for all data tones have been updated, the data tone selection criteria can be reset to perform additional noise estimates for such tones. The updated noise estimates further can be stored, such as in internal memory, for use in subsequent processing.
In a particular aspect of the present invention, the noise estimates for the data tones can be employed in beamforming computations. Because the noise estimates have been decimated in accordance with the present invention, the overhead associated with signal processing requirements for beamforming also are reduced, thereby improving the level of system performance.
The following description and the annexed drawings set forth in certain illustrative aspects of the invention. These aspects are indicative, however, of but a few ways in which the principles of the invention may be employed. Other advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.